CSV File Input

Description

The CSV File Input transform reads data from a delimited file.

The CSV label for this transform is a misnomer because you can define whatever separator you want to use, such as pipes, tabs, and semicolons; you are not constrained to using commas. Internal processing allows this transform to process data quickly. Options for this transform are a subset of the Text File Input transform.

This transform has fewer overall options than the general Text File Input transform, but it has a few advantages over it:

  • NIO — Native system calls for reading the file means faster performance, but it is limited to only local files currently. No VFS support.

  • Parallel running — If you configure this transform to run in multiple copies or in clustered mode, and you enable parallel running, each copy will read a separate block of a single file allowing you to distribute the file reading to several threads or even several slave nodes in a clustered pipeline.

  • Lazy conversion — If you will be reading many fields from the file and many of those fields will not be manipulate, but merely passed through the pipeline to land in some other text file or a database, lazy conversion can prevent Hop from performing unnecessary work on those fields such as converting them into objects such as strings, dates, or numbers.

For information on valid date and numeric formats used in this transform, view the Date Formatting Table and Number Formatting Table.

Options

Option Description

Transform name

Name of the transform.

Filename or the filename field (data from previous transforms)

Specify the name of the CSV file to read from. or Select the fieldname that will contain the filename(s) to read from. If this transform receives data from a previous transform, this option is enabled as well as the option to include the filename in the output.

Delimiter

Specify the file delimiter character used in the target file. Special characters (e.g. CHAR HEX01) can be set with the format $[value], e.g. $[01] or $[6F,FF,00,1F].

Enclosure

Specify the enclosure character used in the target file. Special characters (e.g. CHAR HEX01) can be set with the format $[value], e.g. $[01] or $[6F,FF,00,1F].

NIO buffer size

This is the size of the read buffer. It represents the amount of bytes that is read in one time from disk.

Lazy conversion

The lazy conversion algorithm will try to avoid unnecessary data type conversions and can result in a significant performance improvements if this is possible. The typical example that comes to mind is reading from a text file and writing back to a text file.

Header row present?

Enable this option if the target file’s first line contains a header row with column names. If we mistakenly leave this flag set on files that do not have any columns' names in its first row, Hop will set the column’s name the value found on a specific column for its specific position. In case, for that specific position, the column’s value is empty, Hop will set column’s name to EmptyField_<n> where n is the position of the column in the columns' set. NOTE: remember also to perform a check on the guessed data types and column’s specifier that was set after the file’s analysis because they could be wrong due to wrong assumptions made by Hop while looking at the sample dataset.

Add filename to result

Adds the CSV filename(s) read to the result of this pipeline. A unique list is being kept in memory that can be used in the next workflow action in a workflow, for example in another pipeline.

The row number field name (optional)

The name of the Integer field that will contain the row number in the output of this transform.

Running in parallel?

Check this box if you will have multiple instances of this transform running (transform copies) and if you want each instance to read a separate part of the CSV file(s). When reading multiple files, the total size of all files is taken into consideration to split the workload. In that specific case, make sure that ALL transform copies receive all files that need to be read, otherwise, the parallel algorithm will not work correctly (for obvious reasons). WARNING: For technical reasons, parallel reading of CSV files is only supported on files that don’t have fields with line breaks or carriage returns in them.

File Encoding

Specify the encoding of the file being read.

Fields Table

This table contains an ordered list of fields to be read from the target file.

Preview button

Click to preview the data coming from the target file.

Get Fields button

Click to return a list of fields from the target file based on the current settings (i.e. Delimiter, Enclosure, etc.). All fields identified will be added to the Fields Table.

Metadata Injection Support

You can use the Metadata Injection supported fields with ETL Metadata Injection transform to pass metadata to your pipeline at runtime. The following Option and Value fields of the CSV File Input transform support metadata injection:

  • Options: Filename, Delimiter, Enclosure, NIO Buffer Size, Lazy Conversion, Header Row Present?, Add Filename to Result, The Row Number Field Name, Running in Parallel?, and File Encoding

  • Values: Name, Length, Decimal, Type, Precision, Group, Format, Currency, and Trim Type